Systems have been known that detect unsteady states from images. For example, Japanese Patent Application Laid-open No. 2012-22370 discloses that an unsteady state is specified from an attribute of optical flows in an image. Japanese Patent Application Laid-open No. 2012-22370 specifies that a reverse movement against a flow of a main stream, an abnormal speed state in which a movement with a different speed from those of the other movements is present, and a state in which a turbulence occurs in a flow are the unsteady states.
Such a conventional technique, however, has a limit on types of unsteady states capable of being specified.